Britain faces its greatest risk of terrorist attack yet amid fears that groups may target the general election, according to an annual risk assessment.

There is an "elevated" chance of a strike, while London is at "high" risk, alongside Baghdad and Jerusalem, the study by insurance broker Aon says.

Birmingham, Manchester and Belfast are also deemed to be possible targets.

Terror expert Professor Paul Wilkinson said the study was "misleading" and did not account for national differences.

A map of the global terror threat, which is produced annually by Aon, rates the risk of all forms of attacks to nations as low, guarded, elevated, high or severe.

Election risk

It concludes that Britain is deemed at risk from Islamic extremists, nationalist and separatist groups, organised crime and single-issue organisations, such as those opposed to testing on animals.

Aon terrorism risk consultant Rob Preston said: "While we are certainly not suggesting businesses in London are exposed to the same risks as in Kabul or Baghdad, the threat has increased."

He said: "There may be threats to the general election.

"As we saw in Madrid last year, it is a contemporary tactic and one which terrorists may well claim to have used successfully to influence the result."

Mr Preston also suggested that the return of "those sympathetic to Islamic militancy" to Europe "from places like Iraq" in recent years had helped groups to recruit followers.

To put London in the same category as Baghdad is a nonsense

Professor Paul WilkinsonUniversity of St Andrews

Researchers said the threat of a terrorist strike had increased in 31 countries - nearly half of which were in Western Europe.

And a number of nations which have supported the US-led occupation of Iraq, including Australia, Poland and Estonia, have had their risk rating revised upwards as a result.

Professor Paul Wilkinson, of the Centre for the study of Terrorism and Political Violence at the University of St Andrews, agreed that Britain currently faced an increased risk, but said it was misleading to bracket London with Baghdad.

He said: "It would be foolish to underestimate the possibility of an al-Qaeda attack and because an election is coming up this is a particularly sensitive period.

"However, to put London in the same category as Baghdad is a nonsense."

Professor Wilkinson said the study failed to "take account of the work done by the police and security services on preventing terrorism" which bore "no comparison with somewhere like Baghdad, where there is none of that co-operation or support".